The present invention relates generally to the field of bioremediation. More particularly, it concerns compositions, methods and apparatus for the removal of nitrogenous and halocarbon pollutants from environmental sources including agricultural areas, soils, ground and surface water, sewage, sludges, landfill leachates, and wastewater. In particular embodiments, the invention discloses and claims compositions comprising zero-valent iron and hydrogenotrophic bacteria for use in removing target contaminants by a synergistic combination of abiotic and biological reductive mechanisms.
Various abiotic processes have developed in recent years for the remediation of hazardous environmental pollutants (National Research Council, 1994). One process for abiotic remediation of organic and inorganic pollutants has been developed using zero-valent iron-[Fe(0)] mediated processes.
In this process, as elemental iron is oxidized (corrodes), electrons are released according to the following equations:
Fe0xe2x86x92Fe2++2exe2x80x83xe2x80x83(Equation 1)
These electrons are available for a variety of reduction-oxidation (redox) reactions. Water is reduced to produce hydrogen gas and alkalinity in the form of OHxe2x88x92, with the net reaction resulting in a pH increase:
2H2O+2exe2x88x92xe2x86x92H2+2OHxe2x88x92xe2x80x83xe2x80x83(Equation 2)
Fe0+2H2Oxe2x86x92Fe2++H2+2OHxe2x88x92xe2x80x83xe2x80x83(Equation 3)
Encouraging results in both laboratory and field experiments have stimulated a rapid increase in the use of Fe(0) as a reactive material to treat reducible contaminants (so-called reactive Fe(0) barriers). This approach has been used to degrade waste chlorinated solvents (e.g., Gillham and O""Hannesin, 1994; Johnson et al., 1996; Sweeny, 1980) and nitrate (Till et al., 1998). Reducible heavy metals such as Cr(VI) can also be removed from aqueous solution by reduction to less toxic forms (e.g., Cr(III)) and subsequent precipitation and immobilization, using Fe(0) as the sacrificial metal (Gould, 1982; Khudenko, 1987; Powell et al., 1995; Rickard and Fuerstran, 1968).
Semipermeable reactive Fe(0) barriers have been attractive for groundwater remediation in that they conserve energy and water, and through long-term low operating and maintenance costs, are considerably less costly than conventional cleanup methods. Fe(0) can be placed in the path of a contaminant plume, either on a trench (O""Hannesin and Gillham, 1992), buried as a broad continuous curtain (Blowes et al., 1995), or injected as colloids (Kaplan et al., 1994), to name a few options. However, the efficacy of Fe(0) systems can be limited by (site-specific) slow rates of reaction and by the potential accumulation of products of equal or greater toxicity (Matheson and Tratnyek, 1994; NRC, 1994; Roberts et al., 1996).
Depending upon solution chemistry and pH, Cr(VI) can be present in the form of CrO42xe2x88x92, HCrO4xe2x88x92, H2CrO4, and Cr2O72xe2x88x92. All of this hexavalent chromium species could be reduced to the less toxic, less mobile trivalent form, which is removed from solution as the hydroxide (i.e., Cr(OH)3) under most conditions, using Fe(0) (Gould, 1982; Khudenko, 1987; Powell et al., 1995; Rickard and Fuerstran, 1968):
xe2x80x832Cr6++6exe2x88x92xe2x86x922Cr3+xe2x80x83xe2x80x83(Equation 4)
3Fe0xe2x86x923Fe2++6exe2x88x92xe2x80x83xe2x80x83(Equation 5)
2Cr3++6OHxe2x88x92xe2x86x922Cr(OH)3xe2x80x83xe2x80x83(Equation 6)
2Cr6++3Fe0+6OHxe2x88x92xe2x86x922Cr(OH)3+3Fe2+xe2x80x83xe2x80x83(Equation 7)
The increase in pH caused by iron corrosion (Equation 3) is thus beneficial in removing Cr(III) from solution.
When present in the environment, it is possible for the various species of Cr(VI), and Cr(III) to be sorbed to soils and sediments. It has been shown that Cr(VI) can be reduced to Cr(III) spontaneously by soil organic matter and/or by microorganisms under reducing conditions (Wang et al., 1989; Ishibashi et al., 1990; Yamamoto et al., 1993). Similarly, it has been shown that U(VI) can be reduced to U(IV) by microorganisms (Lovely and Phillips, 1992a and 1992b; Gorby and Lovely, 1992; Thomas and Macaskie, 1996). Once Cr(VI) is reduced to Cr(III) whether by soil organic matter or zero-valent iron, it is highly unlikely (due to kinetic constraints) for it to be oxidized once again. Only in the presence of freshly precipitated manganese oxides (MnO2) or a strong oxidant like Fenton""s reagent (hydroxyl radicals) can Cr(III) be reoxidized.
Fe(0) has shown significant promise in reducing, and thus removing from solution, Cr(VI) (e.g., Blowes et al., 1995; Powell et al., 1995; Gould, 1982). Presently, however, only one field site (Elizabeth City, N.C., Coast Guard site) exists where a reactive Fe(0) barrier is being evaluated to contain and remediate a groundwater plume contaminated with both Cr(VI) and TCE. (Morrison and Spangler, Roy E. West Geotech, Grand Junction, Colo.).
Uranium generally exists as the uranyl cation (UO22+) in soils and groundwaters. It is tightly bound to soil and aquifer media at pH values greater than 6.0. However, it can be complexed by sulfate and organic ligands as well. Longmire et al. (1990) found that the predominant species in acidic uranium mill tailings deposits of New Mexico and Colorado was uranyl disulfate, UO2(SO4)22xe2x88x92; uranyl sulfate aqueous complex, UO2(SO4)0, uranyl divalent cations, and uranyl biphosphate, UO2(HPO4)22xe2x88x92; in that order. Once U(VI) is reduced to U(IV), it becomes much less mobile, similar to chromium. Immobilization is caused by the precipitation of uranium dioxide, and by strong sorption of U(IV) species to soils and sediments. Similar to Cr(III), once uranium has been reduced, it is not likely to become mobilized again unless the pH is reduced or a strong oxidizing agent is encountered. Treatment with zero-valent iron removes dissolved oxygen and increases the pH; both conditions which aid the chemical reduction of chromium and uranium and which keeps them immobilized.
Hexavalent uranium can also be reduced to the less mobile U(IV) form which is removed from solution as the oxide under most conditions:
U6++2exe2x88x92xe2x86x92U4+xe2x80x83xe2x80x83(Equation 8)
U4++4OHxe2x88x92xe2x86x92UO2+2H2Oxe2x80x83xe2x80x83(Equation 9)
Here again, the increase in pH caused by Fe(0) corrosion (Equation 3) is conducive to U(IV) precipitation from solution (Lovely and Phillips, 1992a; Morrison et al., 1995; Thomas and Macaskie, 1996).
Unfortunately, no reports in the literature describe the use of reactive Fe(0) barriers to reduce and remove U(VI), although a pilot facility in Durango, Colo., is presently being tested (S. Morrison of Roy E. West Geotech, Grand Junction, Colo.).
Polychlorinated organics can also be reduced using the exe2x88x92 generated by iron corrosion by replacing Cl atoms with hydrogen atoms. This form of reductive dechlorination is termed hydrogenolysis (Vogel et al., 1987). Using carbon tetrachloride (CT) as an example, first chloroform (CF) and then dichloromethane (DCM) are formed:
CCl4+2exe2x88x92+H+xe2x86x92CHCl3+Clxe2x88x92xe2x80x83xe2x80x83(Equation 10)
CHCl3+2exe2x88x92+H+xe2x86x92CH2Cl2+Clxe2x88x92xe2x80x83xe2x80x83(Equation 11)
Several researches have shown that DCM is a xe2x80x9cdead-endxe2x80x9d product of abiotic treatment of CT or CF with Fe(0) (Helland et al., 1995; Matheson and Tratnyek, 1994). Thus, while abiotic processes are able to reduce some organic compounds, the process often results in endproducts which are toxic, themselves. As such, there are limitations to the use of abiotic processes alone in the remediation of organic compounds from the environment.
TCE is reportedly converted to ethene by hydrogenolysis using Fe(0), generally without the build-up of intermediates (Orth and Gillham, 1996), although trace amounts of chlorinated acetylenes could be formed by TCE dihaloelimination (Roberts et al., 1996). A simplified stoichiometry for TCE hydrogenolysis would be:
CHClxe2x95x90CCl2+6exe2x88x92+3H+xe2x86x92CH2xe2x95x90CH2+3Clxe2x88x92xe2x80x83xe2x80x83(Equation 12)
3Fe0xe2x86x923Fe2++6exe2x88x92xe2x80x83xe2x80x83(Equation 13)
CHClxe2x95x90CCl2+3Fe0+3H+xe2x86x92CH2xe2x95x90CH2+3Fe2++3Clxe2x88x92xe2x80x83xe2x80x83(Equation 14)
Unfortunately, the fact that each of the above reactions is thermodynamically feasible does not guarantee that the reactions are feasible for the removal of such compounds from solution using only abiotic processes. The contaminants must be sufficiently reactive that suitable transformation take place during the time the contaminated groundwater flows through the treatment zone. Moreover, observed removal rates may reflect a number of processes other than chemical reaction at the Fe(0) surface, including mass transport to the surface, adsorption of reactants, and desorption and mass transport of products from the surface (Helland et al., 1995). A positive correlation has been suggested between the mixing rate in batch reactors and reductive dechlorination rate (Matteson and Tratnyek, 1984), presumably due to faster mass transport resulting from the decreased thickness of the diffusion layer. That removal rates might be mass transfer rather than reaction limited, suggests the importance of enhancing contact between Fe(0) and the target contaminant.
Biotic reduction of Cr(VI) and U(VI) may be indirect or direct. Microbes can be indirectly responsible for metal reduction by producing relatively strong reductants like H2S from SO42xe2x88x92 and Fe(II) from Fe(III). In most cases, abiotic reduction using H2S and Fe(II) is much slower than direct biotic reduction (Kriegman-King and Reinhard, 1994; Doong and Wu, 1992). A number of studies have shown that several microorganisms can directly (intracellularly) reduce Cr(VI) to Cr(III) using Cr(VI) as an electron acceptor during microbial respiration (Wang et al., 1989; Ishibashi et al., 1990; Yamamoto et al., 1993). Similarly, it has been shown that U(VI) can be reduced to U(IV) by microorganisms (Lovely and Phillips, 1992a and 1992b; Gorby and Lovely, 1992; Thomas and Macaskie, 1996). For the most part, metal reductases have been implicated in these studies. However, there is evidence that such metals can be used as electron acceptors for growth (Ormerod, 1991). These organisms, GS-15 and Shewanella putrefaciens, can also use nitrate and Fe(III) as terminal electron acceptors.
It has also been shown that a variety of microbes can catalyze the reduction of many chlorinated hydrocarbons. A variety of chlorinated aliphatic hydrocarbons are biotransformed by pure and mixed methanogenic (Bagley and Gossett, 1996; Bouwer et al., 1981; Bouwer and McCarty, 1983; Gossett, 1985; Egli et al., 1987; Hughes and Parkin, 1996; Krone et al., 1989a;b; Mikesell and Boyd, 1990) and non-methanogenic, anaerobic cultures (Egli et al., 1987; Egli et al., 1988; Galli and McCarty, 1989; Egli et al., 1990; Fathepure and Tiedje, 1994). Unfortunately, however, with most biological reactions, when reductive dechlorination is the dominant pathway, intermediates will accumulate (e.g., chloroform and dichloromethane from CT biotransformation; vinyl chloride and the dichloroethenes from TCE and PCE biotransformation). These metabolites are often of more concern than the parent compounds, and thus, the art remains limited with respect to biological treatment of chlorinated hydrocarbons. It should be noted, however, that tetrachloroethene (PCE) and TCE can be used as electron acceptors for growth of some anaerobic organisms with the end products being ethene or ethane (Holliger et al., 1993; Holliger, 1995; Scholz-Muramatsu et al., 1995).
Anaerobic conditions are required to produce the H2 from F(0) corrosion and support the growth of useful anaerobic bacteria. Dissolved oxygen, which may be present is some aquifers, is toxic to anaerobes and may inhibit their activity. Nevertheless, oxygen is quickly depleted by aerobic corrosion of Fe(0) as shown by Helland et al. (1995):
2Fe0+O2+4H+xe2x86x922Fe2++2H2Oxe2x80x83xe2x80x83(Equation 15)
This reaction induces anoxic conditions that are favorable for anaerobic biotransformations.
Chlorinated solvents such as trichloroethylene (TCE), heavy metals such as hexavalent chromium, and radionuclides such as hexavalent uranium, are among the most common contaminants found at DOE sites (Riley et al., 1992). Mixtures of such contaminants have been found in soils and sediments at 11 DOE facilities and in the groundwater at 29 sites. While numerous physical-chemical and biological processes have been proposed to manage DOE contaminated sites, many of these approaches are only marginally cost-effective and/or have detrimental side effects on environmental quality, particularly pump-and-treat processes (National Academy of Science, 1992). Consequently, there is a need to develop improved alternatives for the remediation of sites containing these contaminants.
One alternative was the use of elemental (or zero-valent) iron (Fe(0)) in the development of strictly abiotic processes. Although the reactivity of Fe(0) with chlorinated compounds was recognized as early as 1925 (Rhodes and Carty, 1925), only recently has this process received considerable attention for treating waste chlorinated solvents (e.g., Gillham and O""Hannesin, 1994; Johnson et al., 1996; Sweeny et al., 1980). Reducible heavy metal ions (e.g., hexavalent chromium) and nucleotides (e.g., hexavalent uranium) can also be removed from aqueous solution by reduction and subsequent precipitation using Fe(0) as the sacrificial metal (i.e. xe2x80x9ccementationxe2x80x9d) (e.g., Gould, 1982; Khudenko, 1987; Rickard and Fuerstran, 1968). Results from laboratory and pilot studies awakened considerable national and international interest in the use of Fe(0) as a reactive material (so-called reactive Fe(0) barriers) to minimize subsurface migration of such reducible contaminants. Passive, semipermeable reactive walls are also particularly attractive in that they conserve energy and water, and through long-term low operating and maintenance costs, are considerably less costly than conventional cleanup methods.
Nevertheless, knowledge on the applicability and limitations of reactive Fe(0) barriers is limited, and the feasibility of this process to treat mixtures of chlorinated solvents, heavy metals, and radionuclides has not been demonstrated in the art. One limitation of abiotic reduction with Fe(0) alone to remove some polychlorinated compounds such as carbon tetrachloride is the accumulation of transformation products of equal or perhaps greater toxicity (Helland et al., 1995; Matheson and Tratnyek, 1994; Roberts et al., 1996).
Several reports have suggested that a wide variety of microbes can facilitate reductive dechlorination of polychlorinated organics (see e.g., Bouwer et al., 1981; Krone et al., 1989a;b; Holliger et al., 1993; Vogel et al., 1987). Some microbes have also been shown to facilitate the reduction and immobilization of reducible heavy metal ions, e.g., Cr(VI) (Wang et al., 1989) and radionuclides e.g., U(VI) (Lovely and Phillips, 1992a; 1992b). Anaerobic microorganisms have also been shown to respire nitrate and sulfate originating from waste acids at uranium mill tailings (e.g., Durango, Colo., and Tuba City, Ariz.), which is a major challenge facing the Uranium Mill Tailing Remediation Act (UMTRA) program. However, the availability of appropriate primary substrates has limited the success of these biotic transformations in situ. In particular, many of these contaminants are toxic to a variety of bacterial strains when present at high concentrations, and the rate of remediation by these organisms has been disappointing.
There are several chemical and biological technologies that remove nitrates, and other inorganic compounds as well as organic compounds from water and wastewaters. However, these processes are marginally cost-effective and/or have detrimental side-effects on water quality. For example, physical-chemical processes involving membrane filtration technologies or ion exchange resins are often prohibitively expensive and merely transfer the inorganics, such as nitrates, from one phase to another, thus creating a disposal problem, and creating large quantities of brines.
While biological denitrification processes can convert nitrate to innocuous dinitrogen gas and are typically less expensive, they have adverse side-effects on water quality due to residual organic compounds used to support heterotrophic biological activity and excessive biomass production potentially contaminating the treated water. Therefore, what is lacking in the prior art are effective means for the bioremediation of aqueous environments, particularly with respect to denitrification and the removal of organic compounds such as halocarbons, using systems which do not adversely affect the water quality.
Unfortunately, the efficacy of strictly abiotic processes relying on Fe(0) alone is limited by (site-specific) slow rates of reaction and by the accumulation of products of equal or greater toxicity than the pollutants to be remediated (Matheson and Tratnyek, 1994; NRC, 1994; Roberts et al., 1996). Early work by scientists suggested the coupling of anaerobic oxidation of Fe(0) to a reduction of chloroform was possible using methanogenic bacteria, but no evidence suggested the use of such synergistic processes for inorganic compounds, or organic compounds other than chloroform (Weathers et al., 1995a;b)
The present invention overcomes these and other limitations in the prior art by combining Fe(0) technologies with hydrogenotrophic microorganisms to exploit favorable biogeochemical interactions to detoxifying a variety of inorganic and organic compounds. The inventors"" suprising finding that such biogeochemical interactions could facilitate the reduction of not only inorganic and metal-ion containing compounds, but also haloaromatic, nitroaromatic, and organic pesticides has facilitated a revolutionary advance in the area of microbial-based bioremediation methods. Disclosed and claimed herein are devices and methods for the bioremediation of environmental sites and aqueous solutions using a synergistic combination of biotic and abiotic processes. In particular, the invention concerns iron-supported autotrophic methods which utilize a device comprising a composition containing zero-valent iron and a culture of one or more species of hydrogenotrophic bacteria to remove target contaminants.
In a first embodiment, the invention concerns a device which comprises a composition of zero-valent iron and a culture of one or more hydrogenotrophic bacteria. The hydrogenotrophic bacteria preferably comprise one or more species of bacteria selected from the group consisting of Acetobacterium spp., Achromobacter spp., Aeromonas spp., Acinetobacter spp., Aureobacterium spp., Bacillus spp., Comamonas spp., Dehalobacter spp., Dehalospirillum spp., Dehalococcoide spp., Desulfurosarcina spp., Desulfomonile spp., Desulfobacterium spp., Enterobacter spp., Hydrogenobacter spp., Methanosarcina spp., Pseudomonas spp., Shewanella spp., Methanosarcina spp., Micrococcus spp., and Paracoccus spp. Alternatively, hydrogenotrophic bacteria present in anaerobic sludge or ariaerobic sediments may also be used in the practice of the invention.
Exemplary hydrogenotrophic bacteria include one or more strains of bacteria selected from the group consisting of Acetobacterium woodi, Aeromonas hydrophila, Aeromonas sobria, Alcaligenes eutrophus, Comamonas acidovorans, Dehalococcoide resirictus, Dehalococcoide multivorans, Dehalococcoide ethenogene, Desulfobacterium tiedje, Enterobacter agglomerans, Hydrogenobacter thermophilus, Methanosarcina barkeri, Methanosarcina mazei, Methanosarcina thermophila, Paracoccus denitrificans, Pseudomonas aureofaciens, Pseudomonas maltophilia, Pseudomonas mendocina, and Shewanella putrefaciens. 
In illustrative embodiments, the inventors have shown that hydrogenotrophic bacterial stains such as Paracoccus denitrificans ATCC17741, Paracoccus denitrificans ATCC35512, Paracoccus denitrificans ATCC13543, or Paracoccus denitrificans ATCC19367 are particularly useful in formulating the compositions of the invention. In certain embodiments, the inventors contemplate the use of a mixed culture of one or more of the disclosed microorganisms. Such mixed cultures may comprise two or more hydrogenotrophic organisms, and may also include one or more strains, species, or genera of non-hydrogenotrophic bacteria.
The zero-valent iron of the composition is preferably iron, iron alloy, or iron bimetal. in It may be in the form of metal filings, shavings, turnings, powder, mesh, steel wool, beads, rods, or pellets (exemplary sources include e.g, Malinkrodt, Fisher Scientific, Master Builder, Aldrich Chemical Co., scrap metal suppliers, and the like). Iron bimetallics, composed of a combination of Fe(0) and any of the following: Ni(0), Zn(0), Pt(0), and Pd(0), are also desirable for the compositions and processes of the invention, as are iron-based metallic alloys. The metal may be immobilized in a gel, matrix, or other medium, may be in combination with one or more zeolites or minerals, and may be embedded, or immobilized onto glass, ceramic, cloth, plastic, fiber, non-metal, metalloids, crystals, polymers, and the like. In fact, any formulation of the zero-valent iron which permits contact with or proximity to the hydrogenotrophic bacterial culture, and which permits or facilitates the oxidation of the metal and the liberation of hydrogen gas to be uptaken and utilized by the bacterial culture is contemplated by the inventors to be useful in formulating the particular iron-culture composition.
In preferred embodiments the culture of hydrogenotrophic bacteria (either alone or in combination with other microorganisms) is immobilized, mixed with, or in close proximity to the solid or semi-solid substrate(s) that comprise the Fe(0) compound. The solid substrate may be, but is not limited to, matrices, columns, chromatographic media, glass or plastic beads, plates or surfaces, acrylic beads, acrylamides, polyacrylamides, beaded agarose, Sepharose, tubing, vials, metal supports, mesh, fibers, polymers, ceramics, or cloth and the like. The Fe(0) component may be attached to the solid substrate by any suitable means known to those of skill in the art. Alternatively, the iron itself, or the device housing may serve as a substrate for the growth of the bacterial cells. The device may be a cartridge, a filter, a vessel (including e.g., a reactor, flask, beaker, funnel, bottle, cannister, or tank), a flow-through tubing, radiator, fermenter, or such like. In the case of in situ remediation, the device may be comprised within a system or remediation apparatus, and may comprise a reactive barrier, a membrane, a cylindrical barrier, a gate-and-funnel apparatus, or any other apparatus suitable for placement in an environmental site, and suitable for providing a means for containing the bacterial-Fe(0) composition within the device.
The Fe(0)-containing compound may typically be present at a concentration of from between about 1% and about 99%, more preferably from between about 10% and about 80%, or more preferably from between about 15% and about 50% or so by weight. The iron compound may be alone, or may be added to a porous medium or semi-porous substrate. This medium may contain one or more aluminosilicate minerals (e.g., bentonite, montmorillonite, kaolinite, gibbsite, microline feldspar, albite feldspar) to enhance proton generation at the Fe(0) surface and accelerate corrosion, as described by Powell et al. (1997). The porous medium may also be amended with one or more zeolite minerals to retard the movement of halogenated and nitrated organic contaminants through reactive barriers. This increases both retention time and the removal efficiency. The medium may be formulated to promote adherence by the bacterial culture to the iron substrate, and may be formulated to promote growth or survival of the bacterial culture. Optionally, the medium may be formulated to contain one or more antifungal, antiviral, or antiparasitic agents to retard or prevent the growth of fungi, virus, or parasites in the composition. Also optionally, the composition may be augmented to provide one or more nutrients, vitamins, minerals, or substrates for utilization by the microbial colony. In certain instances, sorbants, such as charcoal, zeolites, or the like, may be added to the composition.
In a second embodiment, the invention provides methods for detoxifying, decontaminating, altering, removing or reducing the concentration of one or more organic or inorganic compounds from an aqueous solution, leachate, runoff, aquifer, groundwater, surface water, well water, an environmental site, soils, and/or agricultural or industrial sources. In particular, compositions and methods are provided for removing, detoxifying, or reducing the concentration of one or more inorganic or organic compound (including nitrates, nitrites, sulfates, sulfites, strontium-, cesium-, chromium- and uranium-containing compounds, halocarbons, haloaromatics, nitroaromatics, and compounds containing one or more nitro- or nitroso-groups) from one or more such site. The methods encompass both in situ and ex situ remediation procedures, and provide both apparatus for large-scale remediation, and devices for remediation of particular pollutants. The inorganic and organic compounds may be naturally occuring pollutants, or may be introduced into the site by the hand of man. The compounds may be present in one or more sites, and may be present in such sites either in pure or nearly-pure form, or may be present along with a plurality of toxic or polluting compounds. Examples of such pollutants may include herbicides, pesticides, industrial chemicals, chemical manufacturing byproducts, byproducts of natural decomposition processes, human or non human wastes, landfill components, mining wastes or runoff, agricultural leachates, industrial runoff, fertilizers and fertilizer byproducts, poisons, and the like. Such pollutants may be present in an enviromental site as the result of a chemical spill, industrial or agricultural accident, pipeline and storage tank failures, derailment of train cars, accidents involving motorized transport of chemicals, explosions, storage tank ruptures, acts of sabotage, and the like.
In an overall and general sense, the methods of the invention generally involve identifying or selecting an aqueous solution or a soil sample or an environmental site that is known to contain, or suspected of containing, or shown to contain, or shown to be susceptible to pollution by, one or more of the inorganic or organic contaminants as disclosed herein, and contacting the solution, soil, or site with a composition comprising a culture of one or more hydrogenotrophic bacteria and a zero-valent iron composition. The aqueous solution may be present in a pipeline, a water or sewage treatment facility, an aqueduct, drainage pond, settling basin, reservoir, storage vessel, or other man-made facility or the like. Alternatively, the aqueous solution may be an environmental site such as a lake, creek, river, stream, aquifer, pond, drainage ditch, or part of an agricultural area, irrigation system, industrial waste facility, landfill, or the like. The environmental site may include any of these areas, and may also include soils, subsurface areas, aquifer recharge zones, leachate areas, embankments in proximity to agricultural sites, water sources, groundwaters, wells, and the like. The environmental site may be defined as, or may be in proximity to, an industrial plant, a treatment plant, a mine, or mining facility, a processing plant, a construction site, a ranch, farm, or cultivated region, a potable or non-potable water supply, a pipeline or utility supply region, sewage facilities, drains, or pipelines, culverts, basins, storm drains, or flood plain control systems. In fact, the inventors contemplate that any site or aqueous solution that is suspected of containing, or is susceptible to pollution by, or is in proximity to a region either contaminated with, or polluted by, one or more inorganic and organic compounds may be a site chosen for remediation using the disclosed methods and compositions.
In certain embodiments, it will be preferable to provide devices which comprise the disclosed compositions to a source to be remediated. This is particularly preferred with the treatment methods are in situ, such as reactive barriers, and the like which are placed into a particular polluted site. Alternatively, where ex situ treatment is desired (e.g., in the treatment of water supplies, pipelines, drainage or collection facilities, storage tanks, sewage treatment plants, etc.) the inventors contemplate the use of the compositions in the manufacture of apparatus and water treatment devices to detoxify such systems. This is particularly desirable in the manufacture of water treatment cartridges, treatment facility machinery, and other apparatus which may be utilized to treat a contaminated sample not present in its native environment.
In one embodiment, the invention provides a method for removing or detoxifying nitroaromatic compounds from an aqueous solution. The method generally involves contacting an aqueous solution suspected of containing a nitroaromatic compound (such as trinitrotoluene, RDX, HMX, 2-aminodintrotoluene, 4-aminodinitrotoluene, and parathion) with a composition consisting of a culture of one or more hydrogenotrophic bacteria and an Fe(0) composition.
In a further embodiment, the invention provides a method for removing or dehalogenating a halocarbon in an aqueous solution. This method generally involves contacting an aqueous solution suspected of containing a halocarbon, such as chlorinated benzenes, trichloroethylene, perchloroethylene, dichloroethylene, vinyl chloride, chloroethane, bromoform, dichlorodifluoromethane, trihalomethanes, tetrachlorodibenzodioxin pentachlorophenol, chlorobenzoates, atrazine, 1,1,1-TCA, CCl4, CHCl3, DCM, or a PCB, with a composition comprising one or more autotrophic bacteria and an Fe(0) composition.
A further aspect of the invention is a method for removing, detoxifying, or reducing the concentration of a poison, herbicide fungicide, nematocide, or pesticide in an aqueous solution or an environmental site. This method generally involves contacting the solution or site suspected of containing such a chemical with a composition comprising one or more hydrogenotrophic bacteria and Fe(0). Exemplary pesticides remediable by these methods include methoxyclor, alachlor, metolachlor, lindane, DDT, DDE, DDD, dieldrin, aldrin, heptachlor, chlordane, 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid and atrazine.
In another embodiment, the invention provides a method for detoxifying, removing or reducing the concentration of redox-sensitive metal ions, such as strontium (II), cesium (I), chromium (VI), uranium (VI), technetium ( ), silver (I), or mercury (II) ions in an aqueous solution or an environmental site. This method generally involves contacting the solution or site suspected of containing one or more of such ions, either free in solution or complexed by organic ligands, with a composition comprising one or more hydrogenotrophic bacteria and Fe(0).
In a further embodiment, the invention provides a method for removing, detoxifying, or reducing the concentration of an inorganic compound such as nitrite, nitrate, sulfite, or sulfate in an aqueous solution or an environemental site. This method comprises contacting the solution or site suspected of containing such an inorganic compound with a composition comprising one or more hydrogenotrophic bacteria and Fe(0).
Another aspect of the invention is a method for reducing a nitroaromatic or a haloaromatic compound in a sample. The method involves selecting or identifying a sample that contains or is suspected of containing one or more such compounds with a composition comprising one or more hydrogenotrophic bacteria and Fe(0).
The present invention further provides methods for the bioaugmentation of in situ reactive permeable barriers, packed or fluidized bed reactors for industrial wastewater or landfill leachate treatment, sand filtration technologies for drinking water treatment, anaerobic digestion for sludge treatment, cylindrical reactive barriers surrounding groundwater wells for well head protection, and combinational approaches using membrane technologies well-known in the art for purification and treatment of water, and in particular, municipal, potable, or water suitable for animal and human consumption.
The efficiency of each method may be calculated as the ratio of the amount of contaminant removed divided by the amount of contaminant initially present in the sample. The rate of decomination may be estimated as the amount of contaminant removed divided by its retention time in the particular treatment zone utilized for remediation. The amount of contaminants present in a site and the amount remaining in a site following treatment may be measured using standard analytical techniques developed for each of the particular contaminants.
The inventors contemplate at least two different approaches for employing the present methods for the bioremediation of water, agricultural extracts or soil leachates, surficial sediments, surface waters, aquifers, groundwaters, springs, and other environmental aqueous areas contaminated with pollutants which are remediable utilizing these methods.
In one embodiment, the invention provides in situ remediation methods, and in particular, the use of permeable and semipermeable barriers. In situ permeable barriers, such as those described in Great Britain Patents GB 2238533A and GB 2255081A represent illustrative embodiments adaptable to the methods of the present invention. The disclosed technique is substantially improved using the present method through the pumping of bacteria either into the groundwater up-gradient from the permeable barrier, or directly into the barrier (FIG. 15A, FIG. 15B, and FIG. 15C). Preferred permeable barrier dimensions range from about 2 to about 6 ft thick, about 25 to about 50 ft long, and from about 15 to about 30 ft deep.
In another embodiment, the invention provides methods and apparatus comprising a treatment wall in a trench. In the simplest case, a trench of the appropriate width can be excavated to intercept the contaminated strata and backfilled with reactive material. The reactive material would consist of Fe(0) mixed with some of the alumniosilicate and/or zeolite minerals and with some anaerobic hydrogenotrophic bacteria mentioned previously (FIG. 2).
Shoring of the trench and use of an appropriate slurry or steel sheet piling may be required for excavation to depths greater than 10 feet. Unlike conventional approaches for groundwater cut-off walls that utilize a soil-bentonite slurry, installation of permeable treatment walls may require the use of biodegradable polymers instead of bentonite or cement to avoid the problem of plugging the wall with residual slurry material (Vidic and Pohland, 1996).
To overcome potential limitations to the life expectancy of the added Fe(0), the reactive media can be placed in the subsurface in removable cassettes, as described by MSE (1996). A temporary sheet pile box or a larger diameter caisson can be installed into the subsurface and the screen panels can be placed on the up- and down-gradient sides, while impermeable panels are placed on the lateral sides. Steel rail guides for the cassettes are installed within this interior compartment and the temporary sheet piles or caisson are removed. The cassette can be a steel frame box (e.g., 8 ft long, 5 ft wide, 1.5 ft thick) with two opposing screened sides and two impermeable sides which is filled with the reactive media and lowered into the cavity. By allowing replacement of cassettes with depleted reactive media, the remediation system operation life can be extended near indefinitely.
In a further embodiment, the invention provides methods and apparatus using an injected treatment zone. A treatment zone which (unlike the treatment wall) is not confined within strict boundaries can be established by using injection wells or by hydraulic fracturing (FIG. 3).
Well systems typically involve injection of fluids or fluid/particulate mixtures for distribution into a treatment zone within the target area of the aquifer (Vidic and Pohland, 1996). Potential advantages of this approach are that there is no need to construct a trench and possible aquifer access at greater depths.
In a further embodiment, the invention provides methods and apparatus using a xe2x80x9cfunnel and gatexe2x80x9d system: In these embodiments, low-permeability cut-off walls (e.g., 10xe2x88x926 cm/s) could be installed with gaps that contain in situ reactive zones (FIG. 4). Cut-off walls (the funnel) modify flow patterns so that groundwater primarily flows through high conductivity gaps (the gates). The cut-off wall could be slurry walls, sheet piles, or solid admixtures applied by soil mixing or jet grouting. The gate would consist of a treatment wall similar to those described above.
Alternatively, in situ remediation may be achieved using barrier technologies such as that of and the compositions of the present invention may also be placed in the path of a contaminant plume, either on a trench (O""Hannesin and Gillham, 1992), buried as a broad continuous curtain (Blowes et al., 1995), or injected as colloids (Kaplan et al., 1994).
In general, these methods involved the use of a large plastic wall or retainer, which is inserted into the subsurface, for example, in a xe2x80x9cfunnel and gatexe2x80x9d design. This method permits the installation and removal of one or more cartridges into the system, without the need for changing the entire system. In this scheme, the inventors contemplate utilizing one or more cartridges which each comprise an Fe(0) substrate and an autotrophic bacterial population. Then, if the bacterial culture or iron substrate needs amending, replenishing, or replacement, the cartridge may be retrieved and a new one re-inserted with fresh substrate and microorganisms. When indicated, natural zeolite materials may be used within the matrix of these reactive barriers to sorb target pollutants and allow for a longer retention time, thus allowing for thinner barriers.
The second general embodiment concerns ex situ treatment methods and devices. Ex situ treatment includes various bioreactor modes and schemes such as sequencing batch reactors (SBR) (FIG. 16), fluidized beds (FIG. 17), and flow-through packed columns (FIG. 18).
The SBR is a periodically operated batch, fill-and-draw reactor containing a support structure for Fe(0) and the bacteria (FIG. 13). Each reactor in an SBR system has five discrete cycles in each cycle. For a nitrate removal scheme these would include, (i) fill/deoxygenate, anaerobic stir and react, (iii) settle, (iv) decant, and (v) idle, cycle adjustment and waste sludge. An advantage of this type of treatment scheme is the flexibility in reaction times depending on the waste being treated. Fluidized bed (FIG. 14) and flow-through packed columns (FIG. 15) are attached growth reactors where contaminated water is continuously pumped through a reactor containing Fe(0) and bacteria. In a fluidized bed reactor, a fine-grained iron would serve as the support media for bacterial growth. Fluidization significantly increases the specific surface area and allows for high biomass concentrations in the reactor. It also reduces the clogging potential when the contaminated fluid contains suspended solids. Flow-through packed column reactors contain Fe(0) support structures to allow for biological growth and attachment.
In general, the inventors contemplate that any apparatus which comprises at least a first inlet port, at least a first outlet port and at least one compartment that comprises an Fe(0)-hydrogenotrophic bacterial composition may be developed to remediate target pollutants from an aqueous solution passed through the device. Exemplary devices include flow-through bioreactors and fluidized bed reactors. These devices may also include cartridges or self-contained modules which form a part of a larger apparatus designed for the treatment of a water source or aqueous supply. Such devices may be combined with other water treatment devices, or may be placed inline with one or more additional water purifying devices as part of an apparatus such as a water purificationsystem, a wastewater or sewage treatment system, or any system designed to remove or reduce the concentration of inorganic and/or organic compounds in an aqueous solution.
Also disclosed is an apparatus for denitrifying an aqueous solution. The apparatus generally consists of one or more devices, each device comprising a culture of one or more autotrophic bacteria, an Fe(0) composition, and a container means for contacting the solution with the bacteria in the presence of the Fe(0) composition in such a device. Exemplary apparatus include sequencing bactch reactor, a continuous culture system, a water treatment plant, a sewage treatment facility, a water purifying system, a wastewater treatment facility, or a detoxification system for aqueous solutions.
A further aspect of the invention is a semipermeable reactive barrier used for denitrifying groundwater in situ. This device generally consists of an in-ground barrier onto which a culture of one or more autotrophic bacteria and an Fe(0) composition is provided. The groundwater is in contact with the bacteria and the Fe(0) composition, such that the pollutants present in the water are remediated via the synergistic abiotic and biotic processes disclosed herein. Illustrative examples of compounds which may be remediated by such devices include nitrogen- or sulfur-containing compounds such as nitrate, nitrite, sulfate, and sulfite, and compounds containing one or more redox-sensitive metal ions such as mercury, strontium, technetium, silver, cesium, chromium, and uranium.
The present further provides compositions for use in the apparatus and devices used in situ and ex situ for the remediation of toxic compounds from aqueous environments. Such Fe(0)-bacterial compositions are useful in devices such as flow-through reactors, biofermenters, reactive barriers, packed or fluidized bed reactors, and the like which are useful in the practice of the methods disclosed herein.
The solid support used in the composition may be in the form of an apparatus or device which comprises a chamber, one or more inlet ports, one or more outlet ports, and a matrix within the chamber to which the Fe(0) and bacterial cells are in proximity. In an illustrative embodiment, the inventors passed a solution containing nitrate over a column containing Fe(0) and a culture of autotrophic denitrifying bacteria, and nitrate was removed from solution via the combined biotic/abiotic processes which occurred in the flow-through bioreactor.